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// Copyright 2019 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package container
import (
"encoding/json"
"fmt"
"io/ioutil"
"os"
"path/filepath"
"sync"
"github.com/gofrs/flock"
"gvisor.dev/gvisor/pkg/log"
)
const stateFileExtension = ".state"
// StateFile handles load from/save to container state safely from multiple
// processes. It uses a lock file to provide synchronization between operations.
//
// The lock file is located at: "${s.RootDir}/${s.ID}.lock".
// The state file is located at: "${s.RootDir}/${s.ID}.state".
type StateFile struct {
// RootDir is the directory containing the container metadata file.
RootDir string `json:"rootDir"`
// ID is the container ID.
ID string `json:"id"`
//
// Fields below this line are not saved in the state file and will not
// be preserved across commands.
//
once sync.Once
flock *flock.Flock
}
// List returns all container ids in the given root directory.
func List(rootDir string) ([]string, error) {
log.Debugf("List containers %q", rootDir)
list, err := filepath.Glob(filepath.Join(rootDir, "*"+stateFileExtension))
if err != nil {
return nil, err
}
var out []string
for _, path := range list {
// Filter out files that do no belong to a container.
fileName := filepath.Base(path)
if len(fileName) < len(stateFileExtension) {
panic(fmt.Sprintf("invalid file match %q", path))
}
// Remove the extension.
cid := fileName[:len(fileName)-len(stateFileExtension)]
if validateID(cid) == nil {
out = append(out, cid)
}
}
return out, nil
}
// lock globally locks all locking operations for the container.
func (s *StateFile) lock() error {
s.once.Do(func() {
s.flock = flock.NewFlock(s.lockPath())
})
if err := s.flock.Lock(); err != nil {
return fmt.Errorf("acquiring lock on %q: %v", s.flock, err)
}
return nil
}
// lockForNew acquires the lock and checks if the state file doesn't exist. This
// is done to ensure that more than one creation didn't race to create
// containers with the same ID.
func (s *StateFile) lockForNew() error {
if err := s.lock(); err != nil {
return err
}
// Checks if the container already exists by looking for the metadata file.
if _, err := os.Stat(s.statePath()); err == nil {
s.unlock()
return fmt.Errorf("container already exists")
} else if !os.IsNotExist(err) {
s.unlock()
return fmt.Errorf("looking for existing container: %v", err)
}
return nil
}
// unlock globally unlocks all locking operations for the container.
func (s *StateFile) unlock() error {
if !s.flock.Locked() {
panic("unlock called without lock held")
}
if err := s.flock.Unlock(); err != nil {
log.Warningf("Error to release lock on %q: %v", s.flock, err)
return fmt.Errorf("releasing lock on %q: %v", s.flock, err)
}
return nil
}
// saveLocked saves 'v' to the state file.
//
// Preconditions: lock() must been called before.
func (s *StateFile) saveLocked(v interface{}) error {
if !s.flock.Locked() {
panic("saveLocked called without lock held")
}
meta, err := json.Marshal(v)
if err != nil {
return err
}
if err := ioutil.WriteFile(s.statePath(), meta, 0640); err != nil {
return fmt.Errorf("writing json file: %v", err)
}
return nil
}
func (s *StateFile) load(v interface{}) error {
if err := s.lock(); err != nil {
return err
}
defer s.unlock()
metaBytes, err := ioutil.ReadFile(s.statePath())
if err != nil {
return err
}
return json.Unmarshal(metaBytes, &v)
}
func (s *StateFile) close() error {
if s.flock == nil {
return nil
}
if s.flock.Locked() {
panic("Closing locked file")
}
return s.flock.Close()
}
func buildStatePath(rootDir, id string) string {
return filepath.Join(rootDir, id+stateFileExtension)
}
// statePath is the full path to the state file.
func (s *StateFile) statePath() string {
return buildStatePath(s.RootDir, s.ID)
}
// lockPath is the full path to the lock file.
func (s *StateFile) lockPath() string {
return filepath.Join(s.RootDir, s.ID+".lock")
}
// destroy deletes all state created by the stateFile. It may be called with the
// lock file held. In that case, the lock file must still be unlocked and
// properly closed after destroy returns.
func (s *StateFile) destroy() error {
if err := os.Remove(s.statePath()); err != nil && !os.IsNotExist(err) {
return err
}
if err := os.Remove(s.lockPath()); err != nil && !os.IsNotExist(err) {
return err
}
return nil
}
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